Transition Metal Complexes and Their Applications in Energy Conversion

Abstract

The rich coordination chemistry of transition metals renders them of interest for broad applications in energy conversion. For example, there is increasing interest in molecular light absorbers such as dye-sensitized photoelectrochemical solar cells (DSSCs) and hybrid inorganic/organic devices. Additionally, the properties of light emitting molecules are the subject of intense research, with applications in organic light emitting diodes (OLEDs) and photosensitisers of energy- and electron-transfer for solar energy conversion.
This thesis can be broadly separated into two sections; (1) the study of a macrocyclic cobalt complex and its potential as a catalyst for the conversion of protons into H2 and (2) the synthesis and study of transition metal complexes as phosphorescent dopants for OLEDs.
In part 1, the synthesis and characterisation of a series of cobalt compounds coordinated by the macrocyclic biquinazoline ligand, Mabiq, is presented. The solution and solid-state structures of the compounds were examined, alongside the electronic structures of paramagnetic 2 and 3. Electrochemistry data reveals that the reduction of 4 is possible to form a formally Co0 species, which shows promise in its activity with respect to H2 production.
In part 2, the synthesis and characterisation of a range of mono- and bimetallic Pt(II) and Ir(III) complexes is presented. A series of readily synthesised tridentate proligands and their resulting complexes is presented that include pseudo-cyclometallating units to allow for mild reaction conditions. The complexes are weakly emissive, with PLQYs in the range 0.1 – 4%, attributed to varying rates of non-radiative decay. Two successful strategies in decreasing non-radiative decay are reported: the replacement of the chloride ancillary ligand with a stronger field acetylide ligand and the development of tetradentate proligands to improve the rigidity of the square planar complexes. The synthesis of hydrazone-based proligands, which offer two N^N^O-coordination sites bridged by a central pyrimidine ring is also reported. Coordination of a second Ir(III) centre results in a 6-fold enhancement of the PLQYs.